returns the resulting slice, also of type <code>S</code>.
The values <code>x</code> are passed to a parameter of type <code>...T</code>
where <code>T</code> is the <a href="#Slice_types">element type</a> of
<code>S</code> and the respective
<a href="#Passing_arguments_to_..._parameters">parameter passing rules</a> apply.
As a special case, <code>append</code> also accepts a first argument